package org.demo.url;

import java.io.*;
import java.net.*;
/**
 * Description:
 * <br/>Copyright (C), 2008-2010, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
//定义下载从start到end的内容的线程
class DownThread extends Thread
{
    //定义字节数组（取水的竹筒）的长度
    private final int BUFF_LEN = 32;
    //定义下载的起始点
    private long start;
    //定义下载的结束点
    private long end;
    //下载资源对应的输入流
    private InputStream is;
    //将下载到的字节输出到raf中
    private RandomAccessFile raf ;

    //构造器，传入输入流，输出流和下载起始点、结束点
    public DownThread(long start , long end
            , InputStream is , RandomAccessFile raf)
    {
        //输出该线程负责下载的字节位置
        System.out.println(start + "---->"  + end);
        this.start = start;
        this.end = end;
        this.is = is;
        this.raf = raf;
        try {
            System.out.println("is的长度:"+is.available());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public void run()
    {
        try
        {
            is.skip(start);
            raf.seek(start);
            //定义读取输入流内容的的缓存数组（竹筒）
            byte[] buff = new byte[BUFF_LEN];
            //本线程负责下载资源的大小
            long contentLen = end - start;
            //定义最多需要读取几次就可以完成本线程的下载
            long times = contentLen / BUFF_LEN + 4;
            //实际读取的字节数
            int hasRead = 0;
            for (int i = 0; i < times ; i++)
            {
                hasRead = is.read(buff);
                //如果读取的字节数小于0，则退出循环！
                if (hasRead < 0)
                {
                    break;
                }
                raf.write(buff , 0 , hasRead);
            }
        }
        catch (Exception ex)
        {
            ex.printStackTrace();
        }
        //使用finally块来关闭当前线程的输入流、输出流
        finally
        {
            try
            {
                if (is != null)
                {
                    is.close();
                }
                if (raf != null)
                {
                    raf.close();
                }
            }
            catch (Exception ex)
            {
                ex.printStackTrace();
            }
        }
    }
}
public class MutilDown
{
    public static void test()
    {
        final int DOWN_THREAD_NUM = 4;
        final String OUT_FILE_NAME = "javarumen_jb51net2.rar";
        InputStream[] isArr = new InputStream[DOWN_THREAD_NUM];
        RandomAccessFile[] outArr = new RandomAccessFile[DOWN_THREAD_NUM];
        try
        {
            //创建一个URL对象
            URL url = new URL("http://wangshuo.jb51.net:81/201206/books/javarumen_jb51net.rar");
            //以此URL对象打开第一个输入流
            isArr[0] = url.openStream();
            long fileLen = getFileLength(url);
            System.out.println("网络资源的大小" + fileLen);
            //以输出文件名创建第一个RandomAccessFile输出流
            outArr[0] = new RandomAccessFile(OUT_FILE_NAME , "rw");
            //创建一个与下载资源相同大小的空文件
            /*for (int i = 0 ; i < fileLen ; i++ )
            {
                outArr[0].write(0);
            }*/
            outArr[0].setLength(fileLen);
            //每线程应该下载的字节数
            long numPerThred = fileLen / DOWN_THREAD_NUM;
            //整个下载资源整除后剩下的余数
            long left = fileLen % DOWN_THREAD_NUM;
            for (int i = 0 ; i < DOWN_THREAD_NUM; i++)
            {
                //为每个线程打开一个输入流、一个RandomAccessFile对象，
                //让每个线程分别负责下载资源的不同部分。
                if (i != 0)
                {
                    //以URL打开多个输入流
                    isArr[i] = url.openStream();
                    //以指定输出文件创建多个RandomAccessFile对象
                    outArr[i] = new RandomAccessFile(OUT_FILE_NAME , "rw");
                }
                //分别启动多个线程来下载网络资源
                if (i == DOWN_THREAD_NUM - 1 )
                {
                    //最后一个线程下载指定numPerThred+left个字节
                    new DownThread(i * numPerThred , (i + 1) * numPerThred + left
                            , isArr[i] , outArr[i]).start();
                }
                else
                {
                    //每个线程负责下载一定的numPerThred个字节
                    new DownThread(i * numPerThred , (i + 1) * numPerThred
                            , isArr[i] , outArr[i]).start();
                }
            }
            /*int length=0;
            for(int i=0;i<isArr.length;i++){
                length+=isArr[i].available();
            }
            System.out.println(length);*/
        }
        catch (Exception ex)
        {
            ex.printStackTrace();
        }
    }
    //定义获取指定网络资源的长度的方法
    public static long getFileLength(URL url) throws Exception
    {
        long length = 0;
        //打开该URL对应的URLConnection。
        URLConnection con = url.openConnection();
        //获取连接URL资源的长度
        long size = con.getContentLength();
        length = size;
        return length;
    }
}
